Second-Language Fluency Predicts Native Language Stroop Effects: Evidence from Spanish-English Bilinguals

Studies have shown reduced Stroop interference in bilinguals compared to monolinguals defined dichotomously, but no study has explored how varying degrees of second language fluency, might affect linguistic inhibitory control in the first language. We examined effects of relative English fluency on the ability to inhibit the automatic reading response on the Golden version of the Stroop Test administered in Spanish. Participants were 141 (49% male) adult native Spanish speakers from the U.S.-Mexico border region (education range = 8-20 and age range = 20-63). A language dominance index was calculated as the ratio of English words to total words produced in both languages using the Controlled Oral Word Association Test with letters PMR in Spanish and FAS in English. Greater degree of English fluency as measured by the dominance index predicted better speed on the Stroop incongruent trial independent of education effects. On the other hand, neither the dominance index nor education predicted performance on the word reading and color-naming trials. These results suggest an advantage in inhibitory control among those with greater second-language ability.